In-situ cap and method of fabricating same for an integrated circuit device

ABSTRACT

An in-situ cap for an integrated circuit device such as a micromachined device and a method of making such a cap by fabricating an integrated circuit element on a substrate; forming a support layer over the integrated circuit element and forming a cap structure in the support layer covering the integrated circuit element.

RELATED APPLICATIONS

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/800,821 filed Mar. 7, 2001, hereby incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to an in-situ cap for an integratedcircuit device such as a micromachined device and to a method of makingsuch an in-situ cap.

BACKGROUND OF THE INVENTION

[0003] Conventional caps for integrated circuit devices such asmicromachined devices are often used to protect and isolate. Typicallythe caps are made independently of the device itself and then attachedafter the device fabrication is completed. Often the cap is fabricatedfrom silicon and fastened to the devices with an organic adhesive orwith an inorganic glass or metal. While this approach can besatisfactory, it does require separate processes to make the caps andthen to join them to the integrated circuit devices. One set of joiningprocesses applies caps to integrated circuit devices before the wafersare singulated. This requires expensive wafer scale processes andequipment. Cap stress effects can cause yield loss if the process is nottightly controlled. However, a tightly controlled wafer level processprotects the delicate micromachined devices early in the manufacturingprocess. Another set of processes applies the caps after singulation.This can be simpler to implement but it requires special precautions toavoid contamination during wafer singulation and other process steps.Still another approach eliminates the requirement for directly attachingcaps to the integrated circuit devices by mounting and wire bonding thedevices inside cavity packages. In essence, the next level packagebecomes the cap. This method often utilizes expensive hermeticallysealed ceramic or metal packages. It also requires that themanufacturing facility maintain unusual cleanliness standards in orderto avoid contamination during assembly of the delicate micromachineddevices.

SUMMARY OF THE INVENTION

[0004] It is therefore an object of this invention to provide animproved in-situ cap for integrated circuit devices includingmicromachined devices and a method of making it.

[0005] It is a further object of this invention to provide such a capand method which utilize the basic integrated circuit fabricationprocess to make the cap as well.

[0006] It is a further object of this invention to provide such a capand method which provides the cap as an integrated in-situ part of thedevice itself.

[0007] It is a further object of this invention to provide such a capand method which require no special or independent effort to make orinstall the cap.

[0008] It is a further object of this invention to provide such a capand method in which the cap can be used to preserve a suitableenvironment within the cap such as a gas or liquid fill or a vacuum.

[0009] It is a further object of this invention to provide such a capand method which protects the capped device immediately upon completionof the processing before any further handling including die separation,testing and handling.

[0010] It is a further object of this invention to provide such a capand method which has much lower manufacturing cost.

[0011] It is a further object of this invention to provide such a capand method in which post-processing is made easier because the devicesare less vulnerable since they are capped at the end of wafer processingbefore die cutting.

[0012] It is a further object of this invention to provide such a capand method which requires the same low temperature processing as therest of the integrated circuit.

[0013] The invention results from the realization that a truly improved,more robust, simpler and less expensive in-situ cap for an integratedcircuit device and method of making such a cap can be achieved byfabricating a cap in-situ on an integrated circuit device as a part ofthe integrated circuit fabrication process by forming a support layer onthe integrated circuit device and then forming the cap structure in thesupport layer covering the integrated circuit element.

[0014] This invention features a method of fabricating an in-situ capfor a micromachined device including fabricating a micromachined elementon a substrate with a sacrificial support layer intact and fabricating acap sacrificial support layer over the micromachined element. The capstructure is formed in the sacrificial layers covering the micromachinedelement and the sacrificial layers are removed within the cap structureto release the micromachined element leaving an in-situ cap integralwith the device.

[0015] In a preferred embodiment forming the cap structure may includeforming a cap well around the element. Forming the cap structure mayalso include filling the cap well to form a cap wall and covering thesacrificial layers to form a top connected with the cap wall. The capmay be formed with at least one hole and removing the sacrificial layersmay include introducing a release agent through the hole in the cap. Thesubstrate may be formed with at least one hole and removing thesacrificial layers may include introducing release agent through thehole in the substrate. The cap hole may be closed to seal the cap. Afluid filler may be introduced through the cap hole into the capsurrounding the micromachined element. The cap hole may be closed toseal in the fluid. The cap hole may be small and the surface tension ofthe fluid may prevent its escape. Fabricating a cap may include forminga contact on the cap. The micromachined element may include a switch andthe contact may be a terminal of the switch. Fabricating a cap may alsoinclude forming a gate electrode on the cap for operating the switch.The fluid may be a crosslinkable material; the volume in the cap may bea vacuum; the fluid may modify a surface inside the cap.

[0016] This invention also features a method of fabricating an in-situcap for an integrated circuit device including fabricating an integratedcircuit element on a substrate, forming a support layer over theintegrated circuit element and forming a cap structure in the supportlayer covering the integrated circuit element.

[0017] In a preferred embodiment the method may further include removingthe support layer within the cap structure.

[0018] This invention also features a micromachined device with anin-situ cap including a substrate, a micromachined element on thesubstrate and an in-situ cap integral with the substrate and coveringthe element. There is at least one conductor extending from the elementunder the cap through the substrate to an external terminal.

[0019] In a preferred embodiment, the cap may be filled with liquid; theliquid may be a dielectric. The micromachined element may include aswitch; the cap may include a hole; the micromachined element mayinclude an optical device; and the hole may be an optical port. The capmay include a contact; the micromachined element may include a switch;and the contact may be a terminal of the switch. The cap may include agate electrode for operating the switch.

[0020] This invention also features a micromachined device with anin-situ cap including a substrate, a micromachined element on thesubstrate, and an in-situ cap integral with the substrate covering theelement. The micromachined element may be an optical device and theremay be an optical port for accessing the optical device. In a preferredembodiment, the port may be in the cap.

[0021] This invention also features a micromachined device with anin-situ cap including a substrate, a micromachined element on thesubstrate, and an in-situ cap integral with substrate and covering theelement. There may be a liquid disposed in the cap.

[0022] In a preferred embodiment the liquid may be a dielectric.

[0023] This invention also features an integrated circuit device with anin-situ cap including a substrate, an integrated circuit element on thesubstrate, and an in-situ cap integral with the substrate and coveringthe element. At least one conductor may extend from the element underthe cap through the substrate to an external terminal.

[0024] This invention also features an integrated circuit device with anin-situ cap including a substrate, an integrated circuit element on thesubstrate, and an in-situ cap integral with the substrate and coveringthe element. The integrated circuit element may be an optical device andthere may be an optical port for accessing the optical device.

[0025] This invention also features an integrated circuit device with anin-situ cap including a substrate, an integrated circuit element on thesubstrate, and an in-situ cap integral with the substrate and coveringthe element. A liquid may be disposed in the cap.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other objects, features and advantages will occur to thoseskilled in the art from the following description of a preferredembodiment and the accompanying drawings, in which:

[0027]FIG. 1 is a schematic side elevational sectional diagram of anintegrated circuit device, namely a micromachined device, as it appearsduring the method of this invention just prior to release of thesacrificial support layers in the cap;

[0028]FIG. 2 is a view similar to FIG. 1 after the release of thesacrificial support layer showing the device with in-situ cap accordingto this invention;

[0029]FIG. 3 is a view similar to FIG. 1 in which the micromachinedswitch element includes an additional terminal and counter gate on thecap;

[0030]FIG. 4 is a view similar to FIG. 2 of the device of FIG. 3;

[0031]FIG. 5 is a schematic side elevational sectional view of amicromachined device with in-situ cap according to this invention afterpackaging;

[0032]FIG. 6 is a view similar to FIG. 5 of an integrated circuit devicegenerally with an in-situ cap according to this invention; and

[0033]FIGS. 7A and B are a flow chart of a process according to thisinvention.

PREFERRED EMBODIMENT

[0034] There shown in FIG. 1 a micromachined switch device 10 which hasbeen fabricated in accordance with this invention as it appears justbefore the removal of the sacrificial layers within the in-situ capwhich was formed as a part of the basic processing of the integratedcircuit itself. The fabrication begins with the application of a silicondioxide layer 12 onto silicon substrate 14. A second layer 16 of silicondioxide is laid down on layer 12 and is then masked to permit etching ofthe holes 18 in layer 16. After these holes are etched they are filledwith aluminum to form conductors 20, 20′. These conductors function tomake electrical interconnection between the micromachined element orother integrated circuit element inside of cap 22 and external circuits.The third silicon dioxide layer 24 is formed on layer 16. Layer 24 isnow masked to expose holes 26, 28, 30 and 32 which are then formed byetching. After this another metal layer is deposited on layer 24 leavingexposed holes 26, 28, 30 and 32. This metal, such as Ru, (however anymetal which provides a low and stable resistance would be suitable), issputter deposited approximately 0.1 micron thick. This layer is maskedand etched, the mask is removed and the remaining Ru metal formscontacts to the under-lying Al metal 38, 48 and 50 and at the same timeforms the source 34, gate 36 and drain 38 of the micromachined elementand forms the anchors 42, 44 for the wall 46 of the cap. Also pads 48and 50 constitute the terminals to be wire bonded to external circuits.After this, a first sacrificial layer 52 is formed. Sacrificial layer 52is masked to create hole 70 approximately ⅓ the thickness of thesacrificial layer and then a deposit of a metal such as Ru, (however anymetal which provides a low and stable resistance would be suitable), ismade to fill the hole 70 to create tip contact 72. Sacrificial layer 52is masked again to expose holes communicating with Ru pads 34, 42, 44,48 and 50. A thin layer of Au e.g. 1.0 micron thick, is now formed onthese selected Ru pads, i.e. gold layers 60, 62, 64, 66 and 68. Layer 52is masked once again to expose the space for the beam 74 and for theanchor 76 of micromachined element, switch 40. A gold layer is depositedto create arm 74 and post 76 as shown, and then, a second sacrificiallayer 80 is added. Layer 80 is masked to create holes 82 which areetched right down to the gold layers 62 and 64. After this, layer 80 ismasked to create the top plate 86 of cap 22 and the gold is deposited tofill wall 82 and top 86 to complete the structure of cap 22. In thisparticular embodiment cap 22 is formed with a number of holes 90 whichserve to accept a release agent that is introduced through them torelease the sacrificial layers 52 and 80 inside of cap 22. The phraseintegrated circuit device or micromachined device refers generally tothe assembly 10 whereas the phrase integrated circuit element ormicromachined element refers to the things under the caps, e.g. switch40.

[0035] When this is done, the complete device appears as in FIG. 2. Thiscavity can now be sealed with an epoxy or a similar sealant in holes 90or may be left open. If switch 40, or another micromachined element orother integrated circuit element had optical portions one of more ofholes 90 could be used as an optical port. Alternatively, a hole 92through substrate 14 could be used as an optical access port. Often thecavity 94 formed in cap 22 is to contain a predetermined environmentsuch as a vacuum or an inert gas or a dielectric liquid to assist orenhance the operation of the switch or other micromachined device orintegrated circuit device protected and isolated by cap 22. If this isthe case, it may be desired to seal hole 90 to keep in the fluid or sealthe vacuum. In some cases the holes may be simply made small enough sothat the surface tension of the liquid prevents leakage or evaporation.Alternatively a reactive liquid can be used, for example, such materialcan polymerize to a high molecular weight material or crosslink into agel or solid form: such products would not leak out through the hole.Examples would include reactive silicone gels, epoxies, protein/watersolutions. Alternatively a fluid can be introduced which modifies asurface in the cap such as a surface of the cap or of the micromachineddevice to reduce stiction, passivate or impart some specific chemicalreactivity on the surfaces (biological applications). For example, HMDS(Hexamethyldisilazane) can be vapor deposited for reducing stiction. Ifthe integrated circuit element is not a device that needs to be free tomove the sacrificial layer may not need to be removed. In fact it may bebeneficial to keep it there if, for example, it has optical orelectrical or thermal insulating properties that are desirable and acoefficient of expansion that is compatible or just for support.

[0036] In another embodiment switch 40 a, FIG. 3, may be fabricated as adouble throw switch by forming another contact tip 100 and anothercounter gate electrode 102 directly on cap 22 a. In this case, anotherstep is inserted before the cap is formed. In this step, layer 80 a ismasked to provide the holes 104, 106, in which the Ru can be depositedto create tip contact 100 and counter gate electrode 102. Then therequired steps are performed to create cap 22 a. After removal of thesacrificial layers the device appears as shown in FIG. 4 as a fullyoperable micromachined double throw switch.

[0037] Typically, device 10 or 10 a is die attached at 110, FIG. 5, to apaddle or lead frame 112 whose contacts 114, 116 are wire bonded tocontacts 66 and 68 with the entire device packaged in housing 120. Asindicated previously, the cap and the method of fabricating it is notlimited to micromachined devices, but is equally applicable to othertypes of integrated circuit devices as shown in FIG. 6 where instead ofswitch 40, an integrated circuit element 122 such as an ASIC,microprocessor or the like has been encapsulated by cap 22. In thisparticular case the purpose of the cap instead of just protection orisolation may have been alternatively or in addition to provide aFaraday cage by providing for example a metallized outer layer 124 andgrounding it as at 126 to provide shielding.

[0038] The method for creating the devices of FIGS. 1 and 2 and FIGS. 3and 4 is shown in flow chart form in FIGS. 7A and B beginning withdepositing the first insulator, such as silicon dioxide, step 150,depositing the second silicon dioxide layer 152, and then masking thesecond layer to create holes and deposit, mask and etch a conductorlayer, step 154. The third silicon dioxide layer is deposited and etchedto create holes for the Ru to contact the conductor pads 26, 28, 30, 32,step 156. A metal such as Ru (however any metal which provides a low andstable resistance would be suitable), is deposited, masked and etched toform 34, 36, 38, 42, 44, 48 and 50, step 158. Then the first sacrificiallayer 52 is deposited, step 160. The first sacrificial layer is maskedand etched to create tip contact 72, and masked and etched a second timeto create the holes for the beam anchor 34, cap anchors 42 and 44 andterminals 48, 50 in step 162. The sacrificial layer is masked again andthe Au is deposited to form the beam 74, 76, terminal pads 66, 68 andthe wall anchors 62, 64, steps 164 and 168. The second sacrificial layeris then deposited 80, step 170, and then masked and etched to createholes and deposit the wall 46, and the top of the cap 22 in step 172.Finally a release agent is applied to remove the second and firstsacrificial layers, step 174. In the construction of FIGS. 3 and 4, theadditional steps are added of; masking and etching the secondsacrificial layer 80 to form an upper tip 100 and counter electrode 102,step 176; then depositing a metal such as Ru, (however any metal whichprovides a low and stable resistance would be suitable) masking andetching to define the tip 104 and counter electrode 106, step 178; thiswould be done between steps 170 and 172.

[0039] Further details of the method for creating the device of FIGS. 1and 2 is shown in chart A and for FIGS. 3 and 4 is shown in chart B.CHART A Process Flow for Switch with the In-Situ Cap Basic SwitchProcess Sputter Deposit Ru Metal 0.1 Thick Photolithography Metal-1Defines Source, Gate, Drain Ion Beam Etch Metal-1 {close oversize brace}and Cap anchors Strip Photoresist Sputter Deposit TiW/cu 0.03 um/0.6 umPhotolithography Tip-1 Defines Tip-1 Diameter and Depth Ion Beam EtchTip-1 0.3 um Strip Photoresist {close oversize brace} Sputter DepositTiW/Ru 0.09 um/0.1 um Photolithography Tip-2 Defines Ru Tip Ion BeamEtch Ru Strip Photoresist Photolithography Base Cut Defines beam anchorsand Ion Beam Etch Base cap anchors Strip Photoresist Sputter depositAu/TiW seed 0.1 um/0.03 um Photolithography Interconnect DefinesInterconnect, Bonds Pads, Au Plate Interconnect Cap Anchor 2.0 um StripPhotoresist {close oversize brace} Photolithography Beam Defines Beam AuPlate Bean 5-20 um depends on device Strip Photoresist Add In-Situ CapPhotolithography Cu Plate Defines Cu Spacer layer Plate Cu 1.0 umSputter Deposit TiW 0.03 urn Strip Photoresist {close oversize brace}Photolithography Cap Defines Cap Au Plate Cap 3.0 um Strip PhotoresistRelease Cap and Beam introduce fill fluid Etch TiW 95% H₂O₂/5% NH₄OH 15minutes Etch Cap Cu 75% DlH₂O/25% HNO₃ 60 minutes Etch TiW 95% H₂O₂/5%NH_(4 OH 15 minutes) Etch Cu 75% DIH₂O/25%HNO₃ 60 minutes Etch TiW{close oversize brace} 95% H₂O₂ /5% NH₄OH 15 minutes Evacuate WithVacuum Introduce Fill Fluid Photolithography Cap Seal Define Photoresistover Cap holes

[0040] CHART B Process Flow for the In-Situ Cap with Counter GateElectrode and Upper Tip Basic Switch Process Sputter Deposit Ru Metal0.1 um Thick Photolithography Metal-1 Defines Source, Gate, Drain andCap Ion Beam Etch Metal-1 {close oversize brace} and anchors StripPhotoresist Sputter Deposit TiW/Cu 0.03 um/0.6 um Photolithography Tip-1Defines Tip-1 Diameter and Depth Ion Beam Etch Tip-1 {close oversizebrace} 0.3 um Strip Photoresist Sputter Deposit TiW/Ru 0.09 um/0.1 umPhotolithography Tip-2 Defines Ru Tip Ion Beam Etch Ru Strip Photoresist{close oversize brace} Photolithography Base Cut Defines beam anchorsand Ion Beam Etch Base cap anchors Strip Photoresist Sputter depositAu/TiW seed 0.1 um/0.03 um Photolithography Interconnect DefinesInterconnect, Bond Pads, Au Plate Interconnect Cap Anchor 2.0 um StripPhotoresist {close oversize brace} Photolithography Beam Defines Beam AuPlate Beam 5-20 um depends on device Strip Photoresist Added Cap Processwith gate counter electrode and 2^(nd) tip Photolithography Cu PlateDefines Cu Spacer layer Plate Cu 1.0 um Strip Photoresist SputterDeposit TiW 0.03 um Photolithography 2nd Tip Defines 2^(nd) Tip Ion BeamEtch 0.3 um Strip Photoresist Sputter Deposit Ru {close oversize brace}Photolithagraphy Metal-2 Defines Counter Gate electrode Ion Beam EtchMetal-2 and 2^(nd) Tip Strip Photeresist Sputter Deposit SiO2Photolithography Defines Oxide over Ru to isolate Interconnect Oxide Rufrom Cap Etch Oxide Strip photoresist Photolithography Cap Defines CapAu Plate Cap {close oversize brace} 3.0 um Strip Photoresist Release Capand Beam introduce fill fluid Etch TiW 95% H₂O₂/5% NH₄OH 15 minutes EtchCap Cu 75% DIH₂O/25% HNO₃ 60 minutes Etch TiW 95% H₂O_(2 /5% NH) ₄OH 15minutes Etch Cu 75% DIH₂O/25% HNO₃ 60 minutes Etch TiW {close oversizebrace} 95% H₂/5% NH₄OH 15 minutes Evacuate With Vacuum Introduce FillFluid Photolithography Cao Seal Defines Photoresist over Cap holes

[0041] Although specific features of the invention are shown in somedrawings and not in others, this is for convenience only as each featuremay be combined with any or all of the other features in accordance withthe invention. The words “including”, “comprising”, “having”, and “with”as used herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

[0042] Other embodiments will occur to those skilled in the art and arewithin the following claims:

What is claimed is:
 1. A micromachined device with an in-situ capcomprising: a substrate; a micromachined element on said substrate; anin-situ cap integral with said substrate and covering said device; andat least one conductor extending from said element under said capthrough said substrate to an external terminal.
 2. The micromachineddevice of claim 1 in which said cap is filled with a fluid.
 3. Themicromachined device of claim 2 in which said fluid is a dielectric. 4.The micromachined device of claim 2 in which the fluid is acrosslinkable material.
 5. The micromachined device of claim 2 in whichsaid cap is filled with a gas that modifies at least one surface insidethe cap.
 6. The micromachined device of claim 1 in which saidmicromachined element includes a switch.
 7. The micromachined device ofclaim 1 in which said cap includes a hole.
 8. The micromachined deviceof claim 7 in which said micromachined element includes an opticaldevice and said hole is an optical port.
 9. The micromachined device ofclaim 1 in which said cap includes a contact.
 10. The micromachineddevice of claim 9 in which the micromachined element includes a switchand said contact is a terminal of said switch.
 11. The micromachineddevice of claim 10 in which said cap includes a gate electrode foroperating said switch.
 12. The micromachined device of claim 1 in whichthe volume inside the cap is a vacuum.
 13. A micromachined device withan in-situ cap comprising: a substrate; a micromachined element on saidsubstrate; an in-situ cap integral with said substrate and covering saiddevice; said micromachined element including an optical device and anoptical port for accessing said optical device.
 14. The micromachineddevice of claim 13 in which said port is in said cap.
 15. Themicromachined device of claim 13 in which said cap is filled with afluid.
 16. The micromachined device of claim 15 in which said liquid isa dielectric.
 17. The micromachined device of claim 13 in which said capincludes a contact.
 18. The micromachined device of claim 15 in whichsaid fluid is a crosslinkable material.
 19. The micromachined device ofclaim 15 in which said fluid is a gas and modifies at least one surfaceinside the cap.
 20. The micromachined device of claim 13 in which thevolume inside the cap is a vacuum.
 21. A micromachined device with anin-situ cap comprising: a substrate; a micromachined element on saidsubstrate; an in-situ cap integral with said substrate and covering saiddevice; and a liquid disposed in said cap.
 22. The micromachined deviceof claim 21 in which said liquid is a dielectric.
 23. The micromachineddevice of claim 21 in which said micromachined device includes a switch.24. The micromachined device of claim 21 in which said cap includes ahole.
 25. The micromachined device of claim 24 in which saidmicromachined element is an optical device and said hole is an opticalport.
 26. The micromachined device of claim 21 in which said capincludes a contact.
 27. The micromachined device of claim 26 in whichthe micromachined element includes a switch and said contact is aterminal of said switch.
 28. The micromachined device of claim 27 inwhich said cap includes a gate electrode for operating said switch. 29.A integrated circuit device with an in-situ cap comprising: a substrate;a integrated circuit element on said substrate; an in-situ cap integralwith said substrate and covering said element; and at least oneconductor extending from said element under said cap through saidsubstrate to an external terminal.
 30. A integrated circuit device withan in-situ cap comprising: a substrate; a integrated circuit element onsaid substrate; an in-situ cap integral with said substrate and coveringsaid element; said integrated circuit element including an opticaldevice and an optical port for accessing said optical device.
 31. Aintegrated circuit device with an in-situ cap comprising: a substrate; aintegrated circuit element on said substrate; an in-situ cap integralwith said substrate and covering said element; and a liquid disposed insaid cap.